Determination of methyl mercury in water samples with electromagnetic induction thermal desorption/pyrolysis coupled to atomic fluorescence spectrometry

A novel non-chromatographic method for the pre-concentration and determination of trace methyl mercury in water samples has been proposed. This method included two main steps: (1) The methyl mercury in sample solution was adsorbed on PDMS of the Fe/SiO₂/PDMS bed enrichment column; (2) the analyte was thermally desorbed from the enrichment column and pyrolysed to Hg⁰ in an iron particle bed pyrolysis column by using electromagnetic induction heating technique, and then detected by an on-line coupled atomic fluorescence detector. Several factors affecting the enrichment column preparation and concentration procedure have been investigated and optimised. Under optimal condition, the detection limit (3σ) was 0.2 ng L^–1, along with relative standard deviations of 2.4% (10 ng L^–1, N = 11) for the repeatability study. The enrichment factor obtained was 108. The two standard reference materials (GBW08675, GBW10029) were analysed to validate the present method. This method was successfully applied to the determination of ng L^–1 methyl mercury in water samples.     

Three dimensional parametrization of electromagnetic shower in Alpha Magnetic Spectrometer Ⅱ ECAL

We develop an empirical formula to parameterize the 3-dimension (3D) distribution of electromagnetic showers in the Alpha Magnetic Spectrometer Ⅱ electromagnetic calorimeter(ECAL). The formula was verified by ECAL test beam data in 2002 and found to perform well. The distribution of electron showers in the ECAL are well described by the formula, which has parameters that allow one to determine the 3D shape of electromagnetic showers in the ECAL. We use this formula to correct for lateral energy leakage and dead channels in the ECAL; good results are obtained.     

Ultra‐light carbon nanotube sponge as an efficient electromagnetic shielding material in the GHz range

CVD synthesised CNT flexible sponge with density lower than 0.02 g cm^–3 has been found to serve as high performance EMI shielding material without the aid of any polymer infiltration or impregnation. Due to its extreme lightweight, the specific SE of the CNT‐sponge was found to be as high as 1100 dB cm³ g^–1, having a total SE above 20 dB in the whole 1–18 GHz range, and being able to shield by absorption. The material is the best of our knowledge this specific SE value appears to be the highest reported hitherto. Improved EM absorbers should fulfil the synergic requirements of being low reflective and highly absorptive. In our CNT‐sponges this condition is not satisfied because, although their net absorption ability is strongly remarkable, their high electrical conductivity favours the wave to be reflected at the input interface. Therefore, this sponge material would have a great potential for microwave‐frequency applications that need negligible reflection and great absorption when combined in a multilayered structure that could prevent the wave to be reflected at the input interface. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Levitation of finite‐size electric dipole over epsilon‐near‐zero metamaterial

Following the suggestion of Rodriguez‐Fortuno et al. [Phys. Rev. Lett. 112 , 033902 (2014)], we study the repulsive force acting on a electric dipole placed over a surface of epsilon‐near‐zero (ENZ) metamaterial. The dependence of the repulsive force value on the dipole size has been studied. We show that the effect of finite size drastically affects the values of the repulsive force as compared to the point‐dipole case. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

金属纳米柱天线的快速电磁分析

基于分段正弦基函数和矩量法,通过求解离散电流节点格林函数的封闭解得到金属纳米柱天线激发表面等离子体的阻抗矩阵.与使用其它基函数矩量法相比,该方法可以减少矩阵方程的维数.仿真结果表明:使用此方法只需求解很小的矩阵方程就可以求解出纳米天线表面极化电流,从而实现对纳米天线的散射特征及谐振模式的快速分析;其结果与时域有限差分仿真结果吻合良好且速度具有显著的优势,尤其在计算斜入射问题时计算优势更加明显.本文的方法对文中计算的模型有效,同样为其他形状纳米柱天线和碳纳米管器件散射特性仿真提供了快速有效的电磁分析方法.     

Spectroscopic properties and radiative lifetimes of SiTe:A high-level multireference configuration interaction investigation

The 18 A-S states correlated to the lowest dissociation limit of SiTe were calculated by using a high-level multirefer-ence configuration interaction （MRCI） method, including scalar relativistic and spin-orbit coupling effects. Based on the calculated potential energy curves, the spectroscopic constants of bound states were determined, which are well consistent with previous experimental results. The spin-orbit matrix elements between the A-S states were computed, which lead to an in-deoth understanding, of oerturbations on the electronic state a^3∏. Finally. the transition dioole moments of allowed transitionsA^1∏-X^1∑^＋,E^1∑^＋-X^1∑^＋,a^3∏-d^3△,a^3∏-d^3△,a^∏-a′^3∑^＋,a^3∏-e^3∑^-,and the radiative lifetimes of A^1∏,E^1∑^＋,and a^3∏ were evaluated.     

A numerical study of electromagnetic waves in periodic waveguides

Here are considered time‐harmonic electromagnetic waves in a quadratic waveguide consisting of a periodic dielectric core enclosed by conducting walls. The permittivity function may be smooth or have jumps. The electromagnetic field is given by a magnetic vector potential in Lorenz gauge, and defined on a Floquet cell. The Helmholtz operator is approximated by a Chebyshev collocation, Fourier–Galerkin method. Laurent's rule and the inverse rule are employed for the representation of Fourier coefficients of products of functions. The computations yield, for known wavenumbers, values of the first few eigenfrequencies of the field. In general, the dispersion curves exhibit band gaps. Field patterns are identified as transverse electric, TE, transverse magnetic, TM, or hybrid modes. Maxwell's equations are fulfilled. A few trivial solutions appear when the permittivity varies in the guiding direction and across it. The results of the present method are consistent with exact results and with those obtained by a low‐order finite element software. The present method is more efficient than the low‐order finite element method. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 490–513, 2014     

Analysis of a multi-frequency electromagnetic imaging functional for thin,crack-like electromagnetic inclusions

Recently, a non-iterative multi-frequency subspace migration imaging algorithm was developed based on an asymptotic expansion formula for thin, curve-like electromagnetic inclusions and the structure of singular vectors in the Multi-Static Response (MSR) matrix. The present study examines the structure of subspace migration imaging functional and proposes an improved imaging functional weighted by the frequency. We identify the relationship between the imaging functional and Bessel functions of integer order of the first kind. Numerical examples for single and multiple inclusions show that the presented algorithm not only retains the advantages of the traditional imaging functional but also improves the imaging performance.